What did The Lives of the Saints mean to Ren before and after he left St Anthony's?

Before Ren left Saint Anthony's, The Lives of the Saints meant escape from the pain of punishment and the freedom to explore the fantastic--or miraculous--world of the saints. After he left, rather after he was forced to leave Saint Anthony's, the volume meant comfort. Later, it meant money. After that it meant a memory and a reference point to judge other events by. As events progressed, not to his liking, it meant a marker of a different kind of life.
Ren took the volume after Father John punished him on the "whipping stool." He later told Brother Joseph that he stole it because he wanted to "hear the rest of Saint Anthony's story." He wanted to read about more saints. He wanted to read the stories in the night more than he wanted to eat or to sleep. Before Ren left Saint Anthony's, The Lives of the Saints meant the hope of real miracles.

[H]e'd read about Saint Veronica curing Tiberius with her veil; Saint Benedict flowing water from a rock; Saint Elizabeth, with her apron full of roses. Possessing the book had made what happened inside the pages somehow belong to him. ... He cared for this more than eating. More than sleeping. He finally said, "I wanted the miracles."

After Ren left Saint Anthony's and found what Benjamin really wanted him for, The Lives of the Saints meant continuity with a past that was all he'd ever known, a past with good and bad memories mixed with good and bad opportunities. The volume connected him to a past in which Brother Joseph made the sign of the cross on his forehead and lovingly handed the stolen volume to him as his own, while saying, "Take it with you. It's not stolen anymore."
After a time, the volume came to mean money and survival when Benjamin sold it for five pennies to Mister Jefferies. It also meant a new book to read when Ren traded up for the stolen volume Deerslayer, the setting, story and characters of which seemed to entangle with his heart strings.

[It had] words that pulled at his own heart, as if there were a string tied somewhere inside his chest that ran down into the book and attached itself to the characters....

As actions required of Ren became more entangled in the underbelly of life, The Lives of the Saints meant a memory that was a reference point for understanding and reacting to other events. When Sister Agnes asked if he wanted her to pray for him, he instinctively "could still feel where Brother Joseph had drawn the cross with his thumb ... before he gave over The Lives of the Saints." As Ren's life sinks, The Lives of the Saints raises him up, even with only the memory of the book. The volume meant a marker of a different kind of life, one that he might someday escape back to.